1. Field
An aspect of the present invention relates to a secondary battery, and more particularly, to a secondary battery capable of preventing a short circuit between an electrode terminal and an electrode assembly when a longitudinal compression is applied to the secondary battery.
2. Description of the Related Art
As the miniaturization and lightweight of portable electronic devices make rapid progress, many studies have recently been conducted to develop secondary batteries used as driving power sources of the portable electronic devices. Such secondary batteries are divided into, for example, a nickel-cadmium battery, a nickel-hydrogen battery, a nickel-zinc battery, a lithium secondary battery and the like.
Among them, the lithium secondary battery is rechargeable, compact and large in capacity, and thus is widely applied to high-tech electronic devices because of its high operating voltage and high energy density per unit weight. Such a lithium secondary battery is formed by inserting an electrode assembly together with an electrolyte into a can and then sealing the top of the can with a cap assembly. Here, the electrode assembly includes a positive electrode plate, a negative electrode plate and a separator interposed between the positive and negative electrode plates.
In this case, the electrode assembly is formed by winding the positive electrode plate, the negative electrode plate and the separator. A positive electrode tab is connected to the positive electrode plate to protrude upward from a top portion of the electrode assembly. A negative electrode tab is connected to the negative electrode plate to protrude upward from a top portion of the electrode assembly. In the electrode assembly, the positive and negative electrode tabs are spaced apart from each other at a predetermined interval so as to be electrically isolated from each other.
The cap assembly includes a cap plate, an insulation plate, a terminal plate and an electrode terminal. The cap assembly is coupled to a separate insulation case and seals the can while being coupled to the top opening of the can. Holes for positive and negative electrode tabs are formed at the insulation case. The positive and negative electrode tabs are respectively inserted into the holes so as to prevent a short circuit between an upper portion of the electrode assembly inserted into the can and a lower portion of the cap assembly. The insulation case functions to inhibit a short circuit that may be caused by the contact of the bent negative and positive electrode tabs with an inner wall of the can.
In the lithium secondary battery configured as described above, as its energy density becomes higher, its thickness becomes thinner. Hence, the lithium secondary battery is less resistant to impact and compression. When impact or compression is applied to the lithium battery, ignition and explosion of the lithium secondary battery may occur as a result of deformation of the electrode assembly accommodated in the can, a short circuit between the electrode plates due to the deformation of the electrode assembly, and the like.
This is a problem when the lithium secondary battery is deformed by a longitudinal compression force (in a direction perpendicular to the longitudinal axis), such as in a longitudinal compression test. This test is one of items for stability of the lithium secondary battery. Often, a local pressure is applied to an upper portion of the electrode assembly in the can while the top surface of the can is bent inside the can, thereby resulting in deformation of the electrode assembly in the can and a short circuit between the electrode plates due to the deformation of the electrode assembly.